Nautilus, Palau, 2011

Emporer Nautilus aka Chambered Nautilus. "When seen from above, the shell is darker in color and marked with irregular stripes, which helps it blend into the dark water below. The underside (shown here) is almost completely white, making the nautilus indistinguishable from brighter waters near the surface. … The nautilus shell presents one of the finest natural examples of a logarithmic spiral.” Wikipedia. Paul Humann, et al, Reef Creature Identification (2010), page 405.